diff --git a/nomad/api/base.py b/nomad/api/base.py
index 008671b..22f6e3a 100644
--- a/nomad/api/base.py
+++ b/nomad/api/base.py
@@ -84,6 +84,9 @@ def _query_string_builder(self, endpoint, params=None):
         if not isinstance(params, dict):
             params = {}
 
+        # Remove parameters that are None
+        params = {key: val for key, val in params.items() if val is not None}
+
         if ("namespace" not in params) and (self.namespace and self._required_namespace(endpoint)):
             query_string["namespace"] = self.namespace